A researcher would like to map the location of galE and trpA genes in a new species of bacterium that appears to be closely related to E. coli. He decides to use cotransduction, and generatesnappropriate donor and recipient strains. He is disappointed when cotransduction is not seen in his experiement. What is the most reasonable explanation for this situation?

#Question id: 176

#Unit 1. Molecules and their Interaction Relevant to Biology

A peptide has the sequence Glu–His–Trp–Ser–Gly–Leu–Arg–Pro–Gly. What is the net charge of the molecule at pH 3

#Question id: 177

#Unit 1. Molecules and their Interaction Relevant to Biology

The titration curve of alanine shows the ionization of two functional groups with pKa values of 2.34 and 9.69, corresponding to the ionization of the carboxyl and the protonated amino groups, respectively. The titration of di-, tri-, and larger oligopeptides of alanine also shows the ionization of only two functional groups, although the experimental pKa values are different. The trend in pKa values is summarized in the table. Which of the following is a reason for this shift in pK values

#Question id: 178

#Unit 1. Molecules and their Interaction Relevant to Biology

Given the pKa values of different acidic sites in cysteine, the principal ionic form which will never exist at any pH

#Question id: 179

#Unit 1. Molecules and their Interaction Relevant to Biology

The average molecular weight of the 20 standard amino acids is 138, but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight.  Why?

#Question id: 180

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following statements about aromatic amino acids is correct?

#Question id: 181

#Unit 1. Molecules and their Interaction Relevant to Biology

Titration of valine by a strong base, for example NaOH, reveals two pK’s. The titration reaction occurring at pK2 (pK2 = 9.62) is: